In the ferrous and nonferrous molten metals industries, ladles and similar molten metal receivers such as torpedoes and tundishes, receive a charge of molten metal and the metal is later transferred to another vessel, such as to metal casting equipment, where it is cooled and solidified. The receivers for molten metal usually are lined with a refractory material, and it is desirable to preheat a receiver before molten metal is received in the receiver in order to avoid interface solidification of the metal upon contact between the metal and the cold interior surface of the receiver, and also to avoid thermal shock to the refractory liner of the receiver, thus avoiding deterioration of the liner. A preheated ladle also minimizes the heat loss from the molten metal as the metal is transported in the ladle from the furnace to the pouring position, thereby assisting in maintaining the molten metal at a high enough temperature for use in a casting machine or mold.
A common prior art method for heating ladles and other molten metal receivers prior to charging them with molten metal is to direct an open natural gas flame into the open chamber of the ladle. The open flame heating method permits combustion gases from within the ladle chamber to escape to the surrounding atmosphere. This permits a substantial amount of the heat energy to escape without effective use thereof, thus wasting an excessive amount of gas. Moreover, it is difficult to uniformly heat a ladle with an open flame, in that the ladle may be overheated in some areas and not heated sufficiently in other areas. Additionally, after a ladle has been initially heated, it is sometimes desirable to maintain the ladle in its heated condition if the ladle achieves its desired temperature before it is time to introduce the molten metal to the ladle. In this situation the open flame heating procedure continues to waste energy and hot spots are more likely to be formed in the ladle.
Recently, an improved ladle heating system was developed wherein a refractory fiber seal is mounted on a lid and the lid and seal are applied to the rim of a ladle and the open flame was applied through the lid to the ladle chamber. A heat exchanger is used to transfer some of the heat of the exhaust gases to the oncoming air used to support combustion. The fiber seal mounted on the lid is compressible and tends to conform to irregularities in the shape of the rim of the ladle as might be present from a build-up of slag or from chips and cracks in the rim. The structures of this type are disclosed in U.S. Pat. Nos. 4,223,873 and 4,229,211. The invention disclosed herein represents an improvement over recently developed heating systems.